US2387868A - Process for the isomerization of hydrocarbons - Google Patents

Description

Oct. 30, 1945. J. ANDERSON ET AL PROCESS FOR THE ISOMERIZATION OF HYDROCARBONS Filed Dec. 25, 1940 t ny m vwN uEom N LNEO 5:8 E5.

Surnnzr H. McAHis+zr William E. Ross \nvzmors: John Anderson utEuEo @C OQ [$304 Patented Oct. 30, 1945 7 UNITED STATES PATENT OFFICE PROCESS FOR THE ISOMERIZATION OF HYDROCARBON S Application December 23, 1940, Serial No. 371,306

Claims.

liquid phase with a minimum of side reactions and maximum catalyst life.

As is well known, the various saturated hydrocarbons having at least four carbon atoms can exist in a number of isomeric modifications. Thus, the paraffinic hydrocarbons from butane to nonane can exist in the following number of isomeric forms:

. Butan 2 Pentane 3 Hexane 5 Heptane 9 Octane 18 Nonane 35 Notwithstanding the large number of isomeric modifications generally possible, these hydrocarbons as found in natural sources such as petroleum occur almost exclusively in the normal or slightly branched modifications.

A few of the lower saturated aliphatic hydrocarbons, such as butane and pentane, are used to a considerable extent in organic syntheses. etc. By far the most important application of thes hydrocarbons is, however, in fuels for internal combustion engines. Studies of the chemical properties and ignition characteristics of a large number of the possible isomers have shown that certain isomeric modifications are vastly superior to others for these purposes, and that, in general, the naturally-occurring isomers are the least preferred. Normal'pentane, for example, is obtained in large quantities from petroleum. It is chemically quite unreactive and, in view of its poor ignition characteristics, is a poor fuel component for internal combustion engines. The branched modification, isopentane, on the other hand, is much more chemically reactive and may be readily condensed with olefinic hydrocarbons by an alkylation process to produce saturated higher molecular weight hydrocarbons having excellent ignition characteristics. Isopentane is, furthermore, an exceptionally valuable fuel component per se, especially for aviation fuels. In view of the vastly superior properties of isopentane over normal pentane and, in general, more highly branched hydrocarbons over less branched hydrocarbons, a commercially practical method for the conversion of normal pentane to isopentane and for converting the large available quantities of less desirable less branched hydrocarbons to their more highly branched isomers is very desirable.

It has long been known that certain acid-acting metal halides, such as catalysts of the Friedel- Crafts type, exert a strong catalytic influence in hydrocarbon reactions. Aluminum chloride, for example, is one of the most powerful cracking and polymerizing catalysts known and is widely used in the cracking of petroleum hydrocarbons into lower boiling hydrocarbons and the polymerization of olefines to synthetic lubricating oils. The aluminum halides when in the presence of a hydrogen halide are known to also catalyze the isomerization of saturated hydrocarbons under certain conditions. Consequently, considerable work has been done in attempts to provide a practical isomerization process employing these agents. With the exception of the isomerization of n-butane to isobutane, however, the various attempts have met with very little success. Butane, although less reactive, is quite stable and can be treated quite satisfactorily in the vapor phase with certain solid promoted aluminum chloride catalysts. In the case of normal pentane and all higher boiling hydrocarbons, however, it appears necessary to resort to-liquid phase treatment. In the liquid phase treatment several problems arise which have so far not been overcome. Thus, the catalysts quickly attack certain small to appreciable quantities of hydrocarbon types and impurities invariably present in commercial hydrocarbon feeds with the formation of tarry materials which coat the catalyst particles and cause them to agglomerate into relatively inactive thick tarry masses. This, of course, is not confined to the isomerization of paraflin hydrocarbons but takes place likewise in various other processes such as alkylation, poly-- are normally liquid and the catalyst cannot therefore agglomerate into hard sticky lumps.

It has also been proposed in certain cases to employ complex double salts of aluminum chloride and aluminum bromide such as those produced by reacting aluminum chloride or aluminum bromide with such salts as the halides of Na, K, Li, NH4, Ca, Mg, Ba, Ag, Cu, etc. These double salts are normally solid compounds of relatively high melting point and low volatility. They are usually impregnated into a porous carrier material such as pumice, diatomaceous earth or the like, and employed in the solid state. In some cases, however, where high reaction temperatures are practical, it .has also been proposed to employthem in their fused or molten state.

While these substitutes for aluminum chloride and aluminum bromide have certain applications wherein they minimize or prevent the agglomeration of the catalyst into inactive masses and are advantageous in certain processes such as the polymerization of olefines, they are entirely unsuited for practical application in the isomerization of saturated hydrocarbons. The isomerization of saturated hydrocarbons, although cata lyzed by aluminum chloride and aluminum bromide (in the presence of a hydrogen halide), differs from the alkylation of aromatic hydrocarbons, the polymerization of olefines, etc. in certain important respects. The isomerization of saturated hydrocarbons, for instance, is a very difficult reaction to effect in a practical way and is catalyzed only by a very few selected catalysts: Thus, although the isomerization of certain saturated hydrocarbons to small extents has been noted with such catalysts as zirconium chloride, beryllium chloride and molybdenum sulfide under very severe conditions, the only catalysts so far known to effect the isomerization in anything like a practical way are aluminum halides in the presence of a hydrogen halide. Alkylation, polymerization, etc., on the other hand, are reactions which are easily effected with any number of catalytic agents including, for instance, the acids of phosphorus, sulfuric acid, zinc chloride, iron chloride, certain acid clays, etc. It is, therefore,

not surprising that the above-described complex compounds of aluminum chloride and aluminum bromide, although effective for certain of these other reactions, are relatively ineffective in the isomerization of saturated hydrocarbons.

The reason for the low order of activity of these complex compounds and their inability to effectively catalyze the isomerization of saturated hydrocarbons is apparent when it is considered that the active catalyst in the isomerization of saturated hydrocarbons with aluminum chloride and aluminum bromide is not aluminum chloride or aluminum bromide per se, but acid compounds thereof such as HAlCh and HA1BI4. Thus, it has long been known that aluminum chloride and aluminum bromide will catalyze the isomerization of saturated hydrocarbons only when promoted by a hydrogen halide. In the above-described complex compounds of aluminum chloride and aluminum bromide the secondary valence forces required to produce the desired acid compounds are saturated by the other constituent of the complex and little or no active acid compound can form.

The primary object of the present invention is to provide a more advantageous method whereby saturated hydrocarbons may be effectively isomerized in a practical manner with liquid catalysts. A more particular object is to provide a more advantageous method for the isomerization of pentane in the liquid phase. Another more particular object is to provide a more advantageous method for the vapor phase isomerization of butane. Still another more particular object is to provide a practical and highly efficient method whereby the anti-knock characteristics of low boiling saturated hydrocarbon fractions of the nature of gasoline may be appreciated with a minimum consumption of catalyst and minimum degradation. Several distinct advantages of the present process, the realization of which are further objects of the invention, are referred to below in the description of the process.

These objects, we have found, may be realized by treating the appropriate hydrocarbons and/or hydrocarbon fractions under isomerizing conditions with the aid of certain liquid aluminum halide catalysts in which an aluminum halide is combined to a substantial extent with a hydrogen halide as a hydrogen aluminum halide or aluminic acid." Thus, the isomerization is effected with the aid of fused catalysts comprising an aluminum halide-hydrogen halide compound such as HAlCl-l and a metal halide which does not react with the aluminum halide either by addition or metathesis. Catalysts of this type are described and claimed in our copending application, Serial No, 363,676, filed October 31, 1940, of which the present application is a continuation-in-part.

While other aluminum halides may be employed in the present process, anhydrous aluminum chloride is preferred. Aluminum chloride is less expensive, is substantially insoluble in the hydrocarbon reactants, and may be employed with a wider variety of metal halides.

By employing with the aluminum halide only metal halides (by which term we mean to include double halides and mixtures of metal halides) which do not react therewith, the secondary valence forces of the, aluminum halide are preserved for the formation of the desired hydrogen aluminum halide. As a consequence, when these fused mixtures are treated with hydrogen halide, much larger quantities of the active acid compounds are formed and excellent isomerization results.

The melting point-composition diagrams of binary mixtures of the more commonmetal halides with aluminum chloride and aluminum bromide have been determined. In most cases, therefore, it is known which metal halides react with the aluminum halides and which do not. Thus, such metal salts as the halides of Na, K, Li, NHi, Ag, Cu, Ca, Mg, Ba, etc. are per se unsuited and specifically excluded since they form stable double salts of the type described above with the corresponding aluminum halides. Since the metal halides employed do not react with the aluminum halide employed, their mixture with the aluminum halide will form simple eutectics or mixed crystals which can be easily identified bv a simple melting point-composition curve.

In view of the considerable differences in properties between the various aluminum halides, whether or not a particular metal halide, double halide, or mixture of halides is suitable will depend to a considerable extent upon the particular aluminum halide employed. Thus. for example, antimony trichloride is a preferred metal halide when employed with aluminum chloride. Antimony tribromide. on the other hand. cannot be employed per se with aluminum bromide since it forms a double salt of the formula, AlBra-SbBrz, therewith. As examples of metal halides which may be employed with one or more of the aluminum halides may be mentioned the halides of As,

Zr, Nb, Mo, Pd, Sn. Sb, Hf, Ta, W, Tl, Pb, Bi, and U.

While, in general, the catalyst may be prepared with any metal halide or mixture of metal halides which does not react with the aluminum halide, the catalysts prepared with certain metal halides are much superior in the present process than others. Thus, for example, we prefer to employ metal halides or metal halide mixtures having normal boiling oints below about 300 C. Catalysts prepared with these metal halides or mixtures of metal halides are much more advantageous in the present process than catalysts prepared with metal halides having higher normal boiling points in several important respects. For example, when catalysts prepared with these lower boiling metal halides are employed, the used catalyst may be easily recovered and reactivated by a simple distillation treatment, whereas when catalysts prepared from higher boiling metal halides are employed this is practically impossible, and more expensive and ineflicient methods must be resorted to. Also, when catalysts prepared from these lower boiling metal halides are employed the isomerization reactions may be executed at much lower temperatures. This is of particular advantage in the isomerization of saturated hydrocarbons since at lower temperatures the equilibrium between the normal and branched chain isomers is much more favorable and higher conversions may be obtained. Also, of the various available metal halides and mixtures of metal halides employed we generally prefer to choose those which are less soluble in the hydrocarbons involved. While this is not essential, it may allow the isomerization to be effected somewhat more economically. It is to be noted, however, that metal halides which act as halogenating agents are generally unsuited. For this reason, the applicable halides of the metals generally contain the metal in a lower valent state. A preferred metal halide which gives exceptionally desirable catalytic agents with the preferred aluminum halide, aluminum chloride, is antimony trichloride. This metal halide when employed alone or in admixture with other suitable metal halides yields excellent catalysts which are generally superior in their high activities, low solubilities in most reactants, low melting points, low boiling points, and high densities.

In order to effect the isomerization at a practical rate under practical conditions, the aluminum halide should comprise at least 3 mol per cent of the fused halide mixture. Since, furthermore, it is often advantageous to effect the isomerization at appreciably elevated temperatures, it is preferable to limit the activity of the catalyst by employing a molecular excess of the metal halide, i. e. at least one plus mols, and preferably two or more mols, of metal halide or mixture of metal halides for each mol of free aluminum halide. This is important since if catalysts are employed having a molar excess of free aluminumhalide with respect to the other metal halide or mixture of metal halides, they become too vigorous in their action after being treated with a hydrogen halide and when used in a molten state may cause undesirable side reactions, such as degradation, almost exclusively. The relative amounts of the respective metal halides in the catalyst will depend upon the melting point and activity desired in the resulting catalyst. In general, it is desirable to employ mixtures corresponding to or approaching the eutectic mixture. In such cases, however, Where the eutectic composition does not contain sufiicient free aluminum halide and consequently gives catalysts of lowcr-than-desired activity, or contains excessive amounts of free aluminum halide and consequently gives catalysts of higherthan-desired activity, the composition may be adjusted to yield a catalyst having the desired activity and a slightly higher melting point. Thus, for example, excellent catalysts may be prepared from mixtures comprising from about 76 to 97 mol per cent antimony trichloride and 24 to 3 mol per cent aluminum chloride. These prepared from mixtures containing about 9 mol per cent free aluminum chloride are of about the optimum activity and melt to free-flowing liquids at about C. The activity may be increased, however, if desired, by employing mixtures containing'more free aluminum chloride, in which case the melting point of the catalyst is increased somewhat.

As explained above, in order to catalyze the isomerization of these saturated hydrocarbons, it is necessary that the catalysts comprise the active acid compounds of the aluminum halide. In order to form these active compounds the fused mixture of metal halides may be treated in any suitable manner with a hydrogen halide prior to use. The active acid compounds may also be formed conveniently during the isomerization by supplying a hydrogen halide to the 7,

reaction m xture during the reaction. Thus, the hydrogen halide may be added during the process as a liquid, gas or solution. The necessary hydrogen halide may, moreover, be generated in chloride, the preferred hydrogen halide is anhydrous hydrogen chloride.

The hydrogen halide may be employed'with the hydrocarbon feed in amounts from as low as about 0.5 weight per cent up to about 10-25 weight per cent. When higher concentrations of hydrogen halide such as 3% to 8% are employed, it is usually desirable to recover and recycle the excess hydrogen halide.

It is to be noted that, unlike the complex catalyst hitherto proposed for other purposes, the catalysts employed in the present process do not hinder or prevent the formation of the hydrogen aluminum halide compounds but allow these compounds to form and exist in a maximum concentration. Thus, for example, a fused metal halide mixture containing about 6% of aluminum chloride when treated with hydrogen chloride may react to convert from about 5% to 40% of the aluminum chloride to the active hy drogen chloride double compound. The concentration of the hydrogen halide-aluminum halide double compound actually produced in the catalyst depends, of course, upon the partial pressure of hydrogen halide above the catalyst, higher partial pressures of hydrogen halide forming higher concentrations of the double compound and increasing the isomerizing activity of the catalyst. A substantial amount of hydrogen halide'may also be taken up in the metal 1 halide mixture by solution. This tends to increase the effective partial pressure of hydrogen halide in contact with the aluminum halide and favors the formation of the desired active addition compounds. If, for example, 408 grams of normal butane containing about 2% HCl is treated with about 400 grams of a fused catalyst containing about 95% SbCh at a temperature of about 80 C. and a pressure of about 240 p. s. i., it is found that about 2.46 grams of HCl are absorbed by the catalyst. About 1 gram of the absorbed 1101 (or about 40%) is dissolved in the catalyst and may be removed by simple extraction or blowing with nitrogen, whereas about 1.44 grams (or about 60%) of the absorbed I-ICl are retained and are most difficult to remove.

The process of the invention is generally applicable for the isomerization of saturated hydrocarbons such, for example, as butane, pentane, hexane, heptane, octane, cyclohexane, dimethyl cyclopentane and the like. It is particularly advantageous for the isomerization of commercial normally liquid saturated hydrocarbons and saturated hydrocarbon fractions having from four to nine carbon atoms a d boiling in the gasoline boiling range, preferably below 70. C. The hydrocarbon treated need not necessarily be a pure individual hydrocarbon but I may be a mixture of two or more hydrocarbons.

Thus, the invention provides a practical process for converting to isopentane the normal pentane content of commercial hydrocarbon mixtures such as are obtained from natural gas, petroleum distillates, and from cracking higher molecular weight hydrocarbons. Conveniently treated normal pentane-containing mixtures are the so-called amylene-pentane fractions from which the olefines have been substantially removed. The treatment of such mixtures which usually contain only small amounts of isopentane results in very materially increasing their isopentane content and enhancing their value as raw materials in the production of isopentane, alkylation products, aviation gasolines, etc. Technical pentane fractions such as those containing from 70% to 80% normal pentane and from to 20% isopentane may be treated in accordance with the process of the invention and their isopentane content increased up to about 90% without appreciable loss of pentane due to decomposition and while realizing a maximum active life of the catalyst. The process is also especially adapted for the improvement of the ignition characteristics of light gasoline fractions such as cuts of straight run gasoline which may or may not contain pentane. 1

The hydrocarbon or mixture of hydrocarbons treated is, however, preferably substantially free of easily polymerizable materials. Olefines, if present in any appreciable amount, not only tend to polymerize but may also alkylate the saturated hydrocarbon with the formation of un desirable higher boiling products. According to the preferred embodiment of the invention, any olefines or other detrimental impurities in the charge stock are, removed prior to use by a suitable treatment, such as treatment with sulfuric acid orby hydrogenation.

. In order to realize the advantages of the molten catalysts employed in the present isollierization process the isomerization must obviously be executed at temperatures at least as high as the melting point of th mixtures of metal halides employed. In the treatment of butane the isomerization is preferably executed at temperatures below about 200* C. and usually below about C. In the treatment of gasoline fractions somewhat lower temperatures; for instance, temperatures below about C. and usually below about 110 C. are preferred. One advantage of the present isomerization process is that when recycling the catalyst through the reaction zone the desired temperature may be conveniently maintained by adjusting the temperature of the recycled molten catalyst. This is not usually possible in other processes using the double salts mentioned above since these salts are usually too high melting to be employed in the fused state. Also, it is not practical when using the abovedescribed organic complexes since these are easily converted to coke by heating. The desired temperature in the raction mixture may also, of course, be maintained in any conventional manner.

When executing isomerization reactions with aluminum chloride per se, it is usually necessary to employ considerable pressures in order to minimize the loss of catalyst by volatilization. In the present process this is not usually necessary and ordinary pressures may be employed. When operating in the preferred manner wherein the hydrocarbon treated isin the liquid phase, however, a sufficient pressure is employed to maintain the hydrocarbon in the liquid phase. Thus, for example, at the more usual operating temperatures, pressures in the order of from about 1.5 to 20 atmospheres absolute are generally sufficient. These pressures may be produced by the hydrocarbon vapor, or may be produced by the addition of inert gases such as methane, hydrogen, nitrogen or the like.

Under the above-described conditions the isomerization takes place at a very practical rate with a minimum amount of side reactions. The reaction time required depends upon the material being isomerized, the conversions desired, the prevailing temperatures and the efliciency of contact with the catalyst.

When operating with efficient agitation at tem-- peratures in the order of 70-120 C. excellent conversions may be obtained with quite shortcontact times and high throughput rates may be realized. In view of the high activity of the catalysts employed in the present process care should be exercised that the reaction conditions (i. e. contact time, temperatures and pressure) are not chosen to severe. In all cases, and especially in such cases where the hydrocarbon or mixture of hydrocarbons treated contains materials which are susceptible to other reactions under the influence of Friedel-Crafts catalysts, the reaction conditions are adjusted to avoid excessive side reactions.

The process may be executed either in the vapor phase or liquid phase. In the vapor phase process the molten catalyst may be continuously recycled down through one or more reaction towers, preferably provided with baflle plates or filled with an inert packing material, while the hydrocarbon vapors pass countercurrent thereto. The process is most advantageous, however, for the treatment of normally liquid hydrocarbons in the liquid phase. This may be effected in any of the conventional ways, including for example by batch autoclave treatments, by continuous or semi-continuous autoclave treatments, by concurrent or countercurrent passage of the hydrocarbon and molten catalyst through reaction towers, and by circulating the reaction mixture through reaction coils 'or tubes under appropriate conditions.

Particularly appropriate methods which have been developed for efiecting the isomerization according to the process of the invention are illustrated in the attached flow diagram wherein a suitable arrangement of apparatus is shown preliminary separation of thehydrocarbon fraction 'into sub-fractions which are then each treated in the most suitable manner, thelower boiling or normally gaseous fraction being isomerized in the vapor phase and the higher boiling fraction being treated in the liquid phase. It is to be noted that it is not essential that both of the treatments be efiected and that either of the treatments (i. e. the vapor'phase isomerization of the lower boiling fraction or the liquid phase isomerization of the higher'boiling fraction) may be eflected alone. The hydrocarbon feed comprising essentially saturated hydrocarbons is first fed to a suitable fractionating apparatus I wherein it is separated into a lower boiling overhead fraction, preferably consisting essentially of butane, and ahigher boiling bottom or debutanized fraction. The overhead fraction is. refractionated in a suitable fractionating apparatus 2* to separate isobutan'e; The bottom fraction consisting largely of normal butane is fed via pump 3 through suitable heat exchangers 4 and 5 to the treating chamber 6. It will be noticed that the product 'from the treater is'fed into fractionator 2 as well as-the overhead fraction from the fractionator l. Thus, fractionator 2, as shown, serves a double purpose. This is a most advantageous arrangement. In such cases where the overhead fraction from fractionator I contains substantial quantities of non-isomerizable hydrocarbons and in such cases where it is desired to include pentane in th lower boiling fraction from fractionator l, atleast' one more fractionating apparatus is'required and the flow must be altered somewhat. This will be readily carbon isomerate. The separated, hydrogen chloride is removed overhead and recycled to reactor 6, entering the latter with the .hydro carbon feed. A small amount of the overhead from fractionator l0 may bevented ,via outlet I2in order to avoidthe accumulation of. excessive quantities of non-condensable inert gases.

The hydrogen chloride required in th process may be conveniently produced ina small generator such as illustrated near the .topofthe flow diagram. Thus, concentrated sulfuric" acid from a storage tank I3 is fed to acolumn I, packed with a loose inert filler such as pumice'or the like. Muriatic acidfroin storage tank I5 is fed to column M at a somewhat lower point. .Dilute sulfuric acid is continuously withdrawnirom the bottom of the column, and the generated hydrogen' chloride is withdrawn from. the top to a storage tank IS. The hydrogen chloride is fed into th recycled hydrogen chloridefrom .the

overhead 'f'rom fractionator I 0 by afl'small compressor H. The hydrocarbon isomerate' from f-ractionator I0 is preferably passed through a caustic scrubber llandthen is returned t -fractionator 2, as described above, In this way substantially pure isobutane maybe recovered from fractionator' 2; none of theisobutane present-in the feed is passed throughthe reactor; and any ,unisomerized normal butane inthe isomerate is apparent to those skilled in the art. The feed preheated to the' desired temperature in heat exchangers '4 and 5 enters reactors near the bottom in the vapor phase, passes up,- preferably drocarbons is also'pumped to fractionator H) bya compressor H. It will-be noticed that the isom-- erate is first cooled sufllciently to condense the,

major portion of the hydrocarbon and then the condensate and vapors are each separately fed to fractionator I0. There are alternative methods of effecting this step. One is to cool the isomerate further and then feed the total condensateto fractionator ID by a suitable pump. Another is to compress the gaseous isomerate to substantially liquefy same. The method i1- lustrated; however, is considerably more efficient than either of these other methods. In fractionator ID the considerable quantities of hydrogen chloride are separated from the hydrorecycled through the system. Thus, thismethod effects acomplete and continuous isomerization with a minimum ,of apparatus. .Inreactor-i the fluid catalyst, such as described above, is introduced at the top and withdrawn from the bottom, being recirculated via pump 20 through a suitable heat exchanger ,2I. Catalyst to be regenerated may be intermittently or: continuously withdrawn to a'regeneratingretort 22. In retort 22fthe metal halide is distilled from -any alumina, etc, and collectedin a suitable receiver 23. After adjusting the concentration of alumi num chloride in the catalyst in receiver 23, the regenerated catalyst is pumpedvia pump 2 4back to pump 20 in the reactor system.

The bottom fraction from fractionator I is preferably j re-fractionat'ed in a.. suitable frac tionating apparatus 30.' .The fractionation in fractionatortti is preferably adjusted to collect as an overhead product a fraction which ismost susceptible to appreciation by the isomerization treatment. As will ,be noted. from theresultsquoted below it is often foundthatwhereasa total fraction is improved. only slightly. byjan isomerization treatment, certain 'fractions there: of may'bejgreatly improved. It the hydrocarbon fraction is first fractionated, part isomerized, and then the fractions reblended, a much greater im provement in octane number is usually therefore possible. Also, this method considerably reduces the amount ofmaterial to be treatedin order ,to effect agiven'octa'ne' number increase. In -prac-, tice we have found that the overhead from fractionator'30 should usually boil up to about 705', Q, although in some cases somewhat higher end pointssuch. for instance, as 05-15020. are,

usually'not substantially appreciated by'an isomerization treatment, is withdrawn from the system and may, if desired. to be reblended ,with The condensate from fractionathe isomerate. tor 30 is pumped via pump 3 I to reactor 32, being introduced near the bottom concurrent with-theliquid catalyst. The product from treater ,32,

which in this case. comprises both the isomerate.

regenerated catalyst and liquid catalyst, is withdrawn from the top and stratified in separator 33. The catalyst (lower layer) is withdrawn from the bottom, passed through a suitable heat exchanger and recirculated through the reactor 32 via pump 34.

Reactor I2 is preferably provided with some means for insuring intimate contact between the two immiscible liquidphases and the gas phase such, for instancefas 'an inert solid porous material; baiiie plates, 'or the like. The hydrocarhon andgas phase collected in separator 33 is withdrawn from the top and passesto a stripping column IS.

A small amount of gases may be vented via outlet 38. The larger quantity, of hydrogen chloride is pumped back to the reactor via pump 31, entering with the hydrocarbon feed.

Make-up hydrogen chloride, generated as described above, is fed to the recycle system via compressor-i1. The bottom product from striptionator 3| consists'largely of a minor amount of metal halides. It maybe returned to reactor -12 via pump- 4| or may be withdrawn as described above and distilled in retort 22. The maybe returned to reactor 32 via pump 24.

' 'An important advantage of the present'prooess is that no sludge of the usual type is formed and that substantially all of the aluminum ,halide employed is ei'ilciently utilized. A small amount of sludge consisting almost exclusively butane was 41.5% with a contact time of only minutes. By increasing the contact time to .20-30 and 60 minutes the conversions to isobutane were 56%, 60.5% and 63%, respectively.

7 may be increased to 63.5%.

The above-quoted conversions obtainable in the isomerization of a relatively pure butane illustrate the exceptional isomerizing ability of the catalysts employed in the process, since butane is quite unreactive and is one of the most difiicult hydrocarbons to isomerize at a practical rate. In

view of this inertness, however, butane is perhaps the easiest hydrocarbon to isomerize without causing excessive side reactions. From a practical point of view, therefore, the most difiicult hydrocarbons to isomerize are the higher parafiln hydrocarbons and, in particular,'comof spent aluminum halide complexes (probably compounds in which one or more of the halogen atoms of thealuminum halide have beenreplaced by organic radicals) andtar-lik polymers is formed, but this material does not appear to affect either the product or the catalyst.

The catalyst, if not fortified from time to time by the addition of aluminum halide, gradually loses its activity due to the exhaustion of the aluminum halide in the; molten mixture. After a long period of 'use,'usually with periodic adjustment of the aluminum halide concentration, it may become contaminated with small amounts of metal oxidesdu to the decomposition of the metal halides by small amounts of moisture, etc. This does not affect the catalytic activit in any way but'may eventually affect the viscosity of the melt and cause pumping troubles] When metal halides having nonnalboiling points below about 300' C. are employediwith'the alu'minum halide they maybe recovered substantiallyfree from these and any other impurities by simply disk tilling-them. r

The present process for the isomerization of saturated hydrocarbons is particularly advantageous in view ofthe high conversions. obtainable at quite moderate temperatures and pres sures. For instance, in one experiment eighteen batches of a 98 n-butane fraction were treated at a hydrocarbon to catalyst ratio of 521 temperatureof 80 C. and contact time of 30 min-' utes under a partial pressure of hydrogen chlorideof 40p. s. i., and a conversion of 46% to 47% isobutane was obtained throughout with no perceptibledecrease in catalytic activity between bon. In another experiment employing a ternperature of about 100 C.,the conversion to isomercial hydrocarbon fractions such as aviation base stocks and the like. These materials, when treated by prior methods, are invariably degraded and entail severe catalystsludging and poor conversions. The present process, however, in view of its relative freedom from sludging difiiculties is exceptionally advantageous for the treatment of such distillates. Thus, by way of example, a few of the distillateswhich have been successfully reformed (isomerized) by the present process and the change in octane number eifected by such treatment are the following:

' Initial Iinal Boiling octane octane range number number (0. I. R.) (C. I. B.)

Pe ivania straight run geso C.

lash-action 15-70 68. 5 83. 5 Hi h octane hydrogenated aviat n gasoline base stock M40 81. 3 s4. e East Texas straight run gasoline vira ctiona i E Up to 72- 6 88. 0

on are run gasoline fraction Up to 70 73. 5' 86. 6 Celliornia aviation base stock.. 2H 73. 0 76. 0 California aviation base stock (iraction of above) 23-68 71. 0 Bi. 6 Illinois straight run gasoline ,iraction. 70-150 i7. 6 ll. 8

' The fact that thecatalyst when spent may be easily freed of contaminating impurities, refortifled and reused is a particular advantage in the present process, especially in the treatment of commercial hydrocarbon fractions such as the above where small amounts of impurities, etc. tend to shorten the catalyst life. Thus, as an illustrative example of the recovery of a used catalyst, a used antimony trichloride-aluminum chloride catalyst containing about 3.9% carbon as impurities was flash-distilled from a retort. 92% of the catalyst was recovered. The

analytical data on the used catalyst, the reoov-- ered catalyst, and the residue were as follows:

Recovered cetal The small amount of antimony retained inthe residue can, of course, be recovered, if desired,

by dissolution. The recovered catalyst is refortified with fresh aluminum chloride to thede sired concentration and is then equivalent in every respect to the freshly prepared catalyst..

In the foregoing and in the appended claims, for purposes of determining the specified mol ratios, the aluminum halides are considered to have the general formula, Al(Hal)x We claim as our invention:

l. A process for the isomerization vof butane which comprises contacting butane in the substantial absence of olefins under isomerization conditions at a temperature below about 200? C. at which the catalyst is in a moltenstate with an isomerization catalyst consisting of a molten mixture comprising from about '76 to about 97 mol portions of antimony trichloride, about 3 to about 24 mol portions of aluminum chloride, and hydrogen chloride.

2. A process for the isomerization of butane which comprises contacting butane in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chloride, hydrogen chloride and antimony trichloride, the mol ratio of antimony trichloride to aluminum chloride being at least 2:1.

3. A process for the isomerization of butane which comprises contacting butane in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten 1 chloride and a chloride of another metal which does not react with the aluminum chloride under the isomerization conditions, the latter metal chloride being in molecular excess with respect to the aluminum chloride.

5. A process for the isomerization of butane which comprises contacting butane in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting ofa molten mixture comprising an aluminum halide, a hydrogen halide and a halide of another metal which does not react with the aluminum halide under the reaction conditions, the latter metal halide being in molecular excess with respect to the aluminum halide.

6. A process for the isomerization of pentane which comprises contacting pentane in the substantial absence of olefins under isomerization conditions at a temperature below about 130 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising from about 76 to about 97 mol portions of antimony trichloride, about 3 to about 24 mol portions of aluminum chloride and hydrogen chloride.

7. A process for the isomerization of pentane which comprises contacting pentane in the substantial absence of olefins under isomerization conditions at a temperature below about C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chloride, hydrogen chloride and antimony trichloride, themol ratio of, antimony trichloride to aluminum chloride being at least 2:1.

8. A process for the isomerization of pentane which comprises contacting pentane in the substantial absence of olefins under isomerization conditions at a temperature below about 130 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chloride, hydrogen chloride and a chloride of another metal which does not react with the aluminum chloride under the isomerization conditions, the latter metal chloride being in molecular excess with respect to the aluminum chloride.

9. A process for the isomerization of pentane which comprises contacting pentane in the substantial absence of olefins under isomerization conditions at a temperature below about 130 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising an aluminum halide, a hydrogen halide and a halide of another metal which does not react with the aluminum halide under the isomerization conditions, the latter metal halide being in molecular excess with respect to the aluminum halide.

10. A process for iscmerizing hydrocarbons which comprises treating a saturated hydrocarbon fraction boiling essentially below 70 C'. in the substantial absence of olefins under isomerization conditions at a temperature below about 130 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising from about '76 to about 97 mol portions of antimony trichloride, about 3 to about 24 mol portions of aluminum chloride and hydrogen chloride.

11. A process for iscmerizing hydrocarbons which comprises treating a saturated hydrocarbon fraction boiling essentially below 70 C. in the substantial absence of olefins under isomerizationconditions at a temperature below about 130 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chloride, hydrogen chloride and antimony trichloride, the mol ratio of antimon trichloride to aluminum chloride being at least 2:1.

12. A process for iscmerizing hydrocarbons which comprises treating a hydrocarbon fraction consisting essentially of saturated hydrocarbons having from 4 to 9 carbon atoms in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising from about 76 to about 97 mol portions of antimony trichloride, about 3 to about 24 mol portions of aluminum chloride and hydrogen chloride.

13. A process for iscmerizing hydrocarbons which comprises treating a hydrocarbon fraction consisting essentially of saturated hydrocarbons having from 4 to'9 carbon atoms in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chloride, hydrogen chloride and antimony tric'hloride, the mol ratio of antimony trichloride to aluminum chloride being at least 2:1.

14. A process for isomerizing hydrocarbons which comprises treating a hydrocarbon fraction consisting essentially of saturated hydrocarbons having from 4 to 9 carbon atoms in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a. molten state with an isomerization catalyst consisting of a molten mixture comprising aluminum chlorideyhydrogeri chloride and a chloride of another metal which does not react with the aluminum chloride under the isomerization conditions, the latter metal chloride being in molecular excess with'respect to the aluminum chloride.

1 5. A process for isomerizing hydrocarbons which comprises treating a hydrocarbon fraction consisting essentially of saturated hydrocarbons having from 4 to 9 carbon atoms in the substantial absence of olefins under isomerization conditions at a temperature below about 200 C. at which the catalyst is in a molten state with an isomerization catalyst consisting of a molten mixture comprising an aluminum halide, a hydrogen halide and a halide of another metal which does not react with the aluminum halide under the isomerization conditions, the latter metal halide being in molecular excess with repect to the aluminum halide.

JOHN ANDERSON. SUMINER H. MCALLISTER. WILLIAM E. ROSS.

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